For each of the following relations, determine whether the relation is: (i) Reflexive. (ii) Anti-reflexive. (iii) Symmetric. (iv) Anti-symmetric. (v) Transitive. (vi) A partial order. (vii) A strict order. (viii) An equivalence relation. Justify all your answers. You need to have eight answers for each question. a The domain of R is a group of students. Ry if x has earned more credits than y. (NOTE: You can assume there are at least two students who have not earned the same number of credits.) b R is a relation on Z such that Ry if and only if x - y = 3m for some integer m. c The domain R is the set of all cell phone towers in a network. Two towers can communicate if they are within a distance of three miles from each other. Ry if x can communicate with y. (NOTE: You can assume that there are at least two towers that are within three miles of each other.)

Describe precisely the composition of the DEPENDENT weak entitys primary key. Use proper terminology in your answer.

Using a graphics program, develop an entity-relationship diagram for a database application for an Internet bookstore where students buy textbooks from a salesperson and receive invoices for their purchases. Use Figure 5.5 as a guide.

What are referential constraint actions?